linux-kernel - Re: [PATCH RFC bpf-next 0/7] bpf trampoline support "jmp" mode

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Message-ID: <20251114083835.553c9480@gandalf.local.home>
Date: Fri, 14 Nov 2025 08:38:35 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
 andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com,
 song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, mhiramat@...nel.org,
 mark.rutland@....com, mathieu.desnoyers@...icios.com, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH RFC bpf-next 0/7] bpf trampoline support "jmp" mode

On Fri, 14 Nov 2025 17:24:43 +0800
Menglong Dong <menglong8.dong@...il.com> wrote:

> Therefore, we introduce the "jmp" mode for bpf trampoline, as advised by
> Alexei in [1]. And the logic will become this:
>   call foo -> jmp trampoline -> call foo-body ->
>   return foo-body -> return foo

This obviously only works when there's a single function used by that
trampoline. It also doesn't allow tracing of the return side (it's
basically just the function tracer for a single function).

Is there any mechanism to make sure that the trampoline being called is
only used by that one function? I haven't looked at the code yet, but
should there be a test that makes sure a trampoline isn't registered for
two or more different functions?

-- Steve